Thermo-responsive trip free circuit breaker



y 26, 1954 H. F. MALONE ETAL 3,

THERMO-RESPONSIVE TRIP FREE cmcun BREAKER Filed Oct. 7, 1960 2Sheets-Sheet 1 40 INVENTORK HM, F/VaZ re. 7,55 Z'zzyerre .P. Adele? W,y/fbvu 1964 H. F. MALONE ETAL 3, ,873

THERMO-RESPONSIVE TRIP FREE CIRCUIT BREAKER Filed Oct. 7, 1960 2Sheets-Sheet 2 United States Patent 3,134,873 THERMO-RESPONSIVE Till?FREE CIRCUIT BREAKER Homer F. Malone and Eugene D. Lauer, Jackson, Mich,assignors, by mesne assignments, to Mechanical Products, Inc, Jackson,Mich, a corporation of Delaware Filed Oct. 7, 1960, Ser. No. 61,274 3Claims. (Cl. 260-416) This invention relates generally to electriccircuit breakens and more particularly to an improved thermo-responsivetrip free circuit breaker.

Automatic electric circuit breakers are often used to protect branchelectrical circuits having electric motors or other electricallyoperated translating devices connected therein. Such circuit breakersgenerally comprise a pair of separable contacts, a releasable operatingmechanism for effecting separation of the contacts, manual means forefiecting release of the operating mechanism, and a trip deviceresponsive to predetermined conditions in the branch electrical circuitand operable to effect release of the operating mechanism. Release ofthe operating mechanism opens the separable contacts of the circuitbreaker thereby to deenergize the electrically operated device.

Generally, the trip device of such circuit breakers comprises a latchmechanism and a current responsive member operable to effect movement ofthe latch. The latch must be relatively strong mechanically in order toretain the operating mechanism and the separable contacts in the closedcondition with sufficient contact pressure to insure the electricalintegrity of the circuit breaker. However, the latch must be relativelyeasily movable due to a relatively small increment of movement of thecurrent responsive member to lend sensitivity to the circuit breaker.Further, the current responsive member must be sensitive to a relativelysmall increment of current above a preselected maximum and have aphysical response characteristic capable of moving the latch.

The criticalness of the aforementioned seemingly incompatiblerequirements in emphasized in circuit breakers designed for theprotection of relatively low current rating circuits. Circuit breakersheretofore known and used are often impractical for use in such lowcurrent applications wherein relatively rapid and sensitive overloadresponse is required in that they characteristically require arelatively large increment of current above a preselected maximum toeffect response of the trip device. The thermal inertia of, for example,the relatively large bimetallic member often used as current responsivemembers, limits the sensitivity thereof sufliciently to preclude theiruse in circuit breakers designed to protect low current circuits. Also,because in former circuit breaker trip devices latch overlap isrelatively small and the latch force relatively variable, frictionalresistance to unlatching effort causes wide variations in the currentrequired to effect operation of the trip device.

Bimetallic members having a low thermal inertia and a sensitivitysufficiently high to be tactuatable by, for example, an overload currentof one ampere or less, generally do not have sufficient mechanicalstrength to effect release of a latching mechanism. Therefore, becausemany modern electrical circuits, for example, aircraft branch circuits,are designed to carry currents of, for example, 1 ampere or less, thereis a present need for a circuit breaker having a trip device that willrespond quickly and positively to relatively small overloads in such lowcurrent circuits.

Another requirement that preferably is satisfied by such low currentrating circuit breakers is that the circuit breakers be trip free inoperation, or, inother words, that the separable contacts thereof cannotbe manually ice held in the closed condition by movement of a manualoperator to the contacts closed position if an overload conditionpersists in the circuit. Further, such a circuit breaker should becapable of relatively easy calibration and should retain its initialcalibration even though subjected to relatively severe operatingconditions.

Accordingly, one object of the present invention is an improved circuitbreaker for the protection of relatively low current electricalcircuits.

Another object of this invention is to provide a circuit breaker thatoperates substantially instantaneously upon the occurrence of arelatively small current overload thereby to provide protection forequipment subject to damage from extremely small overload currents.

-A further object of this invention is a circuit breaker having a tripdevice including an extensible current carrying wire that substantiallyinstantaneously heats and elongates upon the occurrence of apredetermined current condition to effect release of an actuatingmechanism and separation of a pair of electrical contacts.

it is another object of this invention to provide an im proved circuitbreaker that is trip-free in operation.

Another object is to provide an improved latch structure for an electriccircuit breaker that normally retains a pair of contacts in engagement.

Another object is an improved latch structure that is responsive toeffect release of an operating mechanism for the circuit breaker upon arelatively small movement of a thermally responsive member.

Another object is a circuit breaker having a manual operator that ispushed to close the circuit after it has been electrically ormechanically opened and that is pulled to mechanically open the circuit.

Another object is a circuit breaker which has its component parts sodisposed, and constructed of such materials, that the environmentaltemperature to which it is exposed has a negligible affect upon theadjusted trip value of current.

Another object is a circuit breaker having a relatively effortlessunlatching means that imposes no wearing action upon the latchingmechanism and therefore does not adversely affect calibration of thecircuit breaker.

Other objects and advantages of the present invention will becomeapparent from the following detailed description, claims and drawingswherein:

FIGURE 1 is a fragmentary perspective view of a pair of separablecontacts, an operating mechanism, and trip device for a circuit breakerin accordance with an exemplary embodiment of the present invention;

FIG. 2 is a front view, partially in section, of the structure of FIGURE1 shown in the contacts open condition and mounted in an enclosure;

FIG. 3 is a fragmentary view with the operating mechanism broken away toshow the trip device of the circuit breaker;

FIG. 4 is a view similar to FIG. 2 with the contacts, operatingmechanism and trip device in the contacts closed position; and

FIG. 5 is a cross sectional view taken substtantially along the line 5-5of FIG. 4.

Referring now to the drawings, a circuit breaker 10, in accordance withan exemplary embodiment of the present invention comprises an insulatinghousing 12 for the enclosure and support of the separable contacts,operating mechanism, and trip device of the circuit breaker 10. Thehousing 12 comprises a base portion 14 and a cover portion 16 (FIG. 5)having suitable recesses 18 and barriers 24) for the support of thecomponents of the circuit breaker 10, as will be described.

A pair of terminals 30 and 32 extend outwardly of the housing 12 fromthe interior recess or cavity 18 thereof for connection to an externalelectrical circuit -13 (not shown). The terminal 32 is of L-shapedconfiguration, an upper end portion 34 thereof supporting a fixedcontact 36. The fixed contact 36 is maintained in operative alignmentwith a movable contact 38 that is supported for movement by a contactcarrier 40, in a manner to be described.

As best seen in FIGURE 5, a manual operator 50, made of insulatingmaterial, extends outwardly of and is supported by a tubular collar 52.The collar 52 has a threaded outer end portion 54 so as to be mountablein, for example, a control panel (not shown). The collar 52 has a radialflange 56 at the inner end 58 thereof, the flange 56 having a generallyhexagonal cross sectional configuration to preclude rotation of thecollar 52 in a complementary aperture 60 in the base 14 and cover 16 ofthe circuit breaker 10.

The manual operator 50 has a central cavity 61 (FIGS. 4 and for theacceptance of a folded upper end portion 62 of a contact operating slide70. The end portion 62 of the slide 70 is normally biased against theupper end of the cavity 61 by a helical compression spring 63 thatextends between the end portion 62 of the slide 70 and a folded upperend portion 64 of a manual release slide 65. The folded end portion 64of the slide 65 extends through a rectangular aperture 66 in the slide70 and is normally biased downwardly by the spring 63 against atransversely extending lower end portion 67 of the manual operator (FIG.5). The slide is movable relative to the slide 70 to effect manualopening of the circuit breaker, as will be described. A lower endportion 72 of the slide 70 is supported in a pair of complementaryrecesses '74 and 76 in the base 14 and cover 16, respectively. V V Theslide 70 has a longitudinally extending slot 80 therein for theacceptance of a transversely extending pin 32that is fixedly supportedby the base 14. It is to be noted that the pin 32 also extends through acomplementary slot 83 in the slide 65 (FIG. 5) to permit relativemovement of the slide 65 with respect to the base 14.

An operating spring 84 extends between the fixedly mounted pin 82 and atransverse flange 86 on the slide 70 to normally bias the slide 'itlandmanual operator 5i) outwardly of the housing 12 or, as seen in thedrawings, upwardly with respect to the housing 12 and collar 52. Becausethe end portion 64 is biased against the end portion 67 of the manualoperator 50, the slide 65 is also normally biased upwardly with respectto the housing 12.

The slide 70 has a transversely extending pin 98 secured thereto, as byWelding or staking, for the support of the movable contact carrier 40and a contact actuating spring 92. The spring 92 is supported in anannular groove 94 in the pin (FIG. 5), an end portion 95 thereofengaging the flange 86 on the slide 70 and an opposite end portion 96thereof being engaged in a complementary cutout 98 in the contactcarrier 40. The contact carrier 40 is journaled about the pin 90 forrotation with respect to the slide 7% the spring 92 normally biasing thecontact carrier 40 clockwise, as seen in the drawings, with respect tothe slide 70 to the contacts open position, as seen in FIG. 2.

The contact carrier 40 has a latching surface 100 at an opposite endportion 102 thereof from the movable contact 38 that is engageable undera latching flange 104 on a rotatable latch lever 106. The latch lever106 is pivotally supported on a transversely extending pin 108 that isfixedly supported by the base 14.

As best seen in FIGURE 1, the latch lever 106 has a rearwardly extendingand angularly upwardly facing cam surface 110 supported on an angularlyupwardly extending cam extension 111 for engagement with a complementary cam 112 on a rotatable trip lever 114. The trip lever 114 isjournaled about a transversely extending pin 116 that is fixedlysupported by the base 14.

As best seen in FIGURE 3, the latch lever 106 is normally biased towardthe trip lever 114 by a helical coil spring 120 having end portions 122and 124 engaged in suitable apertures 126 and 128 in the latch and triplevers 106 and 114, respectively. It is to be noted that movement of thelatch and trip levers 106 and 114 toward one another is limited byengagement of the cam 112 on the trip lever 114 with the cam surface 110on the latch lever 106.

The trip lever 114 has an upwardly extending end portion 130 with atransverse flange 132 thereon for the support of an upper end portion134 of an extensible thermal responsive wire 136. A lower end portion138 of the wire 136 is affixed to a calibration plate 140 that issupported in a complementary recess 18 in the base 14. The calibrationplate 140 has a threaded aperture 142 therein for the acceptance of acomplementary calibration screw 144. The screw 144 is supported bysuitable barriers 20 in the base 14, a continual bias thereupon beingmaintained by a leaf spring 146 thereby to position the calibrationplate 140 positively Within the base 14.

The trip lever 114 is normally biased counterclockwise, as seen in thedrawings, about the support pin 116 therefor, by a helical compressionspring 150 that extends between the base 14 and the trip lever 114,being disposed about a suitable car 152 on the trip lever 114 tofacilitate positioning thereof.

It is to be noted that a radius extending between the central axis ofthe pivot pin 116 for the trip lever 114 and the point of attachment ofthe end portion 134 of the Wire 136 to the trip lever 114 is generallyparallel to the line of extension of the wire 136. Therefore, arelatively small increment of elongation of the wire 136 effects a.

relatively large angular movement of the trip lever 114 under the biasof the spring 150. Counterclockwise movement of the trip lever 114effects clockwise movement of the latch lever 106 due to engagement ofthe cam 112 on the trip lever 114 with the cam face 110 on the latchlever 106. It is to be noted that the point of engagement of the cam 112with the cam face 110 is at a relatively small radial distance from thepivotal axis of the latch lever 106 as compared to the radial distanceto the point of engagement between the latching surface 109 on thecontact carrier 40 with the latch 104 on the latch lever 106. Therefore,a relatively small increment of angular movement of the cam surface 110under the bias of the cam 112 effects a relatively large displacementofthe latch 104. In this manner, a relatively small increment ofelongation of the wire 136 effects a relatively large movement of thelatch 104 thereby maximizing overlap between the latch 104 and latchingsurface 100 to insure stability and reliability of the circuit breaker10 in conditions wherein the circuit breaker 10 is subjected to shockand vibration tending to spuriously unlatch the contact carrier 40.

Electrical continuity through the circuit breaker 10 is effected by aflexible conductor that extends from the trip lever 114 to the movablecontact carrier 40. A second flexible conductor extends between theterminal 30 and the calibration plate 140. Therefore, upon closure ofthe contacts 36 and 38, an electrical circuit through the circuitbreaker 10 runs from the terminal 30 through the flexible conductor 162to the calibration plate 140 thence through the extensible wire 136 tothe trip lever 114. The trip lever 114 is electrically connected throughthe flexible conductor 160 to the movable contact carrier 40 thence tothe movable contact 38, fixed contact 36 and terminal 32. 2

Upon the occurrence of an overload in an electrical circuit containingthe circuit breaker 10, the thermoresponsive wire 136 elongates,permitting the trip lever 114 to rotate counterclockwise under thebias'of the spring 150. Counterclockwise rotation of the trip lever 114is transmitted to the latch lever 106 by engagement of the cam 112 onthe trip lever 114 with the cam face 110 on the latch lever 106.Clockwise rotation of the latch lever 106 effects movement of the latch104 away from the latching surface 100 on the contact carrier 40,thereby permitting the contact carrier 40 to rotate clockwise under thebias of the spring 92 and the slide 70 to move upwardly under the biasof the spring 84.

Contraction of the thermo-responsive wire 136 due to cooling thereof,upon the removal of the overload condition that effects heating andelongation thereof, effects movement of the trip lever 114 clockwiseagainst the normal bias of the spring 150. The latch lever 106 followsthe trip lever 114 due to the bias of the spring 120 therebetween.Counterclockwise rotation of the latch lever 106 brings the latch 104thereof into a position where it is conditioned to engage the latchsurface 100 of the contact carrier 40. Subsequent downward movement ofthe slide 70, as by manually pushing on the operator 50, carries thelatch surface 100 to a position under the latch 104, the end portion 102of the contact carrier bypassing the latch 104 due to a camming actionof an angularly orientated cam face 170 on the contact carrier 40.Release of the manual operator 50 permits the slide 70 to move upwardlyunder the bias of the spring 84, bringing the latch surface 100 intoengagement with the latch 104 and the contacts 36 and 38 intoengagement. Contact pressure is thus maintained by the spring 84.

Manual opening of the contacts 36 and 38 is accomplished by pullingoutwardly on the manual operator 50. Because the latching surface 100and contact 38 of the contact carrier 40 are latched against the latch104 and contact 36, respectively, the slide 70 cannot move upwardly withrespect to the housing 12. However, upward movement of the manualoperator 50 is transmitted to the slide 65 through engagement of thelower extension 67 and folded upper end portion 64 thereof,respectively. Outward movement of the manual operator 50 and slide 65with respect to the slide 70 is accommodated by compression of thespring 63. A lower and angularly downwardly extending end portion 180(FIG. 4) of the slide 65 engages a lower edge face 182 of the cam face110 on the latch lever 106 to bias the latch lever 106 clockwise, asseen in the drawings, and disengage the latch 104 from the latchingsurface 100 on the contact carrier 40. Release of the contact carrier 40permits the slide 70 to move upwardly under the bias of the spring 84,and the contact carrier 40 to rotate clockwise under the bias of thespring 92 to the position shown in FIG. 2.

Another feature of the present invention is that the circuit breaker issubstantially self-compensating for changes in ambient temperature.Compensation is accomplished due to the disclosed orientation of theoperating components wherein the member responsive to electricaloverload extends generally parallel and is connected to the trip leverthat is movable upon the occurrence of the overload condition. Thus,changes in ambient temperature effect like incremental elongations ofthe trip lever and thermo-responsive member that cancel each other.

From the foregoing description, it should be apparent that the circuitbreaker of the present invention is responsive to a relatively smallchange in condition of the thermo-responsive member thereby to be wellsuited to the protection of low amperage branch circuits.

It is to be understood that the specific construction of the improvedcircuit breaker herein disclosed and described is presented for thepurpose of explanation and illustration and is not intended to indicatelimits of the invention, the scope of which is defined by the followingclaims.

What is claimed is:

1. An electric circuit breaker for interrupting an electrical circuitupon the occurrence of a predetermined condition therein comprising apair of separable contacts, a releasable operating mechanism foreffecting separation of said contacts, and a trip device for normallyrestraining said operating mechanism and movable to effect release ofsaid operating mechanism upon the occurrence of said predeterminedcondition, said operating mechanism comprising a manual operator havinga contact carrier pivotally supported thereon, said contact carrierhaving one of said separable contacts at one end thereof and a latchingsurface at the other end, said trip device comprising a rotatable triplever, means normally biasing said trip lever in one direction, anelongated latch lever pivotally supported at one end and having a latchat the other end engageable with the latching surface on said contactcarrier to retain said operating mechanism and separable contacts in thecontacts closed condition, said latch lever being normally biasedtowards said trip lever and having a cam surface angularly related toand intermediate a radius drawn between the pivotal support and latchingsurface thereof, and a thermo-responsive elongatable wire having one endattached to said trip lever at a point radial- 1y spaced from thepivotal axis thereof and normally restraining said trip lever frornrotation under the bias of said means, said wire being adjustablysupported at the other end thereof to provide for calibration of saidtrip device and extending at a relatively small angle to a radius drawnbetween the pivotal axis of said trip lever and the point of attachmentof said wire to said lever whereby a relatively small increment ofelongation of wire permits a relatively large angular movement of saidtrip and latch levers about their pivotal axes under the bias of saidmeans thereby to effect disengagement of said latch and latchingsurfaces, release of said operating mechanism and separation of saidcontacts.

2. An electric circuit breaker for interrupting an electrical circuitupon the occurrence of a predetermined condition therein comprising apair of separable contacts, a releasable operating mechanism foreffecting separation of said contacts, a trip device for normallyrestraining said operating mechanism and movable to effect release ofsaid operating mechanism upon the occurrence of said predeterminedcondition, said trip device comprising a rotatable trip lever, meansnormally biasing said trip lever in one direction, a latch levernormally biased towards said trip lever and movable with and withrespect to said trip lever, a thermo-responsive elongatable wireattached to said trip lever at a point radially spaced from the pivotalaxis thereof and normally restraining said trip lever from rotationunder the bias of said means, said wire extending generally normally tothe direction of the movement of the point of attachment thereof to saidtrip lever whereby a relatively small increment of elongation of wirepermits a relatively large angular movement of said trip lever about itspivotal axis under the bias of said means, and manually operable meanscomprising a first slide normally biased towards the contacts openposition and a second slide movable with respect to said firs-t slidetowards the contacts open position to effect movement of said latchlever with respect to'said trip lever thereby to release said operatingmechanism and separate said contacts.

3. An electric circuit breaker for interrupting an electrical circuitupon the occurrence of a predetermined condition therein comprising apair of separable contacts, a releasable operating mechanism foreffecting separation of said contacts, a trip device for normallyrestraining said operating mechanism and movable to effect release ofsaid operating mechanism upon the occurrence of said predeterminedcondition, said trip device comprising a rotatable trip lever, meansnormally biasing said trip lever in one direction, a latch levernormally biased towards said trip lever and movable with and withrespect to said trip lever, a thermo-responsive elongatable wireattached to said trip lever at a point radially spaced from the pivotalaxis thereof and normally restraining said trip lever from rotationunder the bias of said means, said wire extending generally normally tothe direction of movement of the point of attachment thereof to saidtrip lever whereby a relatively small increment of elongation of wirepermits a relatively large angular movement of said trip lever about itspivotal axis underthe biasof said means, a first slide having a contactcarrier pivotally supported thereon with one of said contacts at one endthereof and a latch surface at the other end thereof en- 'gagable withsaid latch lever, said slide being normally 5 biased towards thecontacts open position, and a second slide movable with respect to saidfirst slide towards the contacts open position to effect movement ofsaid latch lever with respect to the latch surface on said contactcarrier thereby to release said operating mechanism and 1 separate saidcontacts.

References Cited in the file of this patent UNITED STATES PATENTSGreenway et 'al. May 3, 1927 Combi Oct. 19, 1937 Ingwersen June 28, 1960FOREIGN PATENTS Germany Dec. 6, 1956

2. AN ELECTRIC CIRCUIT BREAKER FOR INTERRUPTING AN ELECTRICAL CIRCUITUPON THE OCCURRENCE OF A PERDETERMINED CONDITION THEREIN COMPRISING APAIR OF SEPARABLE CONTACTS, A RELEASABLE OPERATING MECHANISM FOREFFECTING SEPARATION OF SAID CONTACTS, A TRIP DEVICE FOR NORMALLYRESTRAINING SAID OPERATING MECHANISM AND MOVABLE TO EFFECT RELEASE OFSAID OPERATING MECHANISM UPON THE OCCURRENCE OF SAID PREDETERMINEDCONDITION, SAID TRIP DEVICE COMPRISING A ROTATABLE TRIP LEVER, MEANSNORMALLY BIASING SAID TRIP LEVER IN ONE DIRECTION, A LATCH LEVERNORMALLY BIASED TOWARDS SAID TRIP LEVER AND MOVABLE WITH AND WITHRESPECT TO SAID TRIP LEVER, A THERMO-RESPONSIVE ELONGATABLE WIREATTACHED TO SAID TRIP LEVER AT A POINT RADIALLY SPACED FROM THE PIVOTALAXIS THEREOF AND NORMALLY RESTRAINING SAID TRIP LEVER FROM ROTATIONUNDER THE BIAS OF SAID MEANS, SAID WIRE EXTENDING GENERALLY NORMALLY TOTHE DIRECTION OF THE MOVEMENT OF THE POINT OF ATTACHMENT THEREOF TO SAIDTRIP LEVER WHEREBY A RELATIVELY SMALL INCREMENT OF ELONGATION OF WIREPERMITS A RELATIVELY LARGE ANGULAR MOVEMENT OF SAID TRIP LEVER ABOUT ITSPIVOTAL AXIS UNDER THE BIAS OF SAID MEANS, AND MANUALLY OPERABLE MEANSCOMPRISING A FIRST SLIDE NORMALLY BIASED